As the communications technology develops continuously, more and more servers are deployed in a network, along with which the server virtualization technology develops rapidly, such that more and more bridges are required, substantially increasing the equipment cost of an operator as well as equipment management cost. To reduce equipment cost and equipment management cost in network deployment, in particular in a data centre network, a port extension technology for bridge is proposed in the industry, namely the investment and management cost for switching equipment are reduced by bridge port extension.
Bridge port extension is implemented by cascade of Port Extender (PE) assembly. FIG. 1 is a flowchart of multicast forwarding of EVB in relevant art, as shown in FIG. 1, the Extended VLAN Bridge (EVB) includes an EVB controlling bridge and a PE assembly connected with a physical port of the EVB controlling bridge. The EVB is connected with a User Equipment (UE) via the PE assembly and an external port of the EVB controlling bridge itself, and there are multiple extended ports inside the PE assembly. When the EVB controlling bridge detects a PE assembly at its physical port, depending on the number of UEs connected with the PE assembly, a port mapping S assembly corresponding to the EVB controlling bridge performs instantiation between a customer assembly (C assembly, in short) and the physical port, to allocate a service VLAN (S-VLAN) identifier (SVID) for a mapping port corresponding to an instance, that is, each physical port connected with the PE assembly will perform instantiation of a corresponding port on assembly C, such that a bridge originally with 3 physical ports is extended into a bridge with 7 exit port. Namely, there is a private virtual channel from the assembly C to each mapping port. After receiving a multicast frame, the assembly C will search for a corresponding mapping port according to a mapping relation between a multicast address and a mapping port bitmap, and forward the multicast frame at each mapping port.
However, because there is only one physical port between the EVB controlling bridge and each PE assembly, the virtualized mapping ports in the EVB controlling bridge actually correspond to the same physical port, such that in a multicast service, the same multicast frame is sent to the same physical port through multiple mapping ports, forwarded to the PE assembly by the physical port, and forwarded by the PE assembly again to each corresponding UE via a downlink port. Therefore, the same multicast frame may be repeatedly duplicated and forwarded at the same physical port, causing tremendous waste of network bandwidth resources.